Build Paho MQTT c library on Mac OS X

This post describes how to build the Paho MQTT library on Mac OS X with
MacPorts openssl.

Prepare your system

Install the compiler

You need Xcode or the Xcode command line utils. If you're not sure if
they are already installed open a terminal and try to run the gcc
command. If you need to install the compiler a popup will appear to do
so.

Install Mac Ports

If not done already download and install the MacPort system and install
the openssl library by executing the following command:

sudo port install openssl

You need at least openssl-1.0.1g_0 to not be affected by heartbleed
bug!

Clone the repository

Get the latest version because there are some improvements done the last
weeks.